This invention relates to apparatus for mechanically assisting circulation of the blood in the human body. The apparatus comprises a pumping chamber in association with a variable flow resistant device or valve directly in the cardiovascular system. According to the invention the apparatus is so positioned in the cardiovascular system that a fully effective pump is formed with the help of the valve functions of the cardiovascular system itself.
Various devices for mechanically assisting circulation of the blood in the human body have been developed in the course of the last twenty years. A primary feature of all these devices is that the diseased heart remains in the body and that its functions are taken over by the assisting device either in toto or more usually only in part (Wolner E.:-Die mechanische Kreislaufunterstutzung in Experiment und Klinik. Weiner klinische Wochenschrift, 84, No. 26, 1972).
From a functional point of view two types of apparatus can be distinguished, namely parallel and series (by-pass and series pass) pumps. The former are parallel to a part of the heart (right or left chamber), the latter are in series therewith. If the whole of the heart is short-circuited (total by-pass) then it is necessary at the same time to reoxygenate the blood because the pulmonary circulation is by-passed. Short period total by-pass has been practiced for many years in cardiac surgery. All these pumps have two openings for the blood stream, viz. an entry and an exit. Some move the blood through valves, others by direct displacement (pinch pumps, roller pumps) in a desired direction. The alternative principle of counterpulsation provides mechanical circulatory relief. Since the heart has a period of rest after each period of work, it is possible during the work period, i.e., during blood ejection (systole) to relieve the pressure in the cardiovascular system, and to introduce energy into the system, i.e., raise the pressure during the period of rest (diastole). This relieves the heart during systole, whereas the required pressure for circulation is mechanically generated during diastole. The particular advantage of counterpulsation is less the relief afforded to the heart than the possibility of properly filling the coronary vessels during diastole. Disregarding short period temporary employment of the total by-pass, i.e., of the heart-lung machine, it can be generally said that circulating pumps are not at present in clinical use, but that the principle of counterpulsation is being employed to an increasing extent.
A major reason for this development is the difficulty of application of the pump because two connections (anastomoses) with the cardiovascular system are needed, whereas in counterpulsation only one of such connection is necessary.
The disadvantage of counterpulsation is the described limited degree of relief afforded to the heart because the pressure in the circulating system may not be arbitrarily reduced during systole. The object of the present invention is to overcome this disadvantage.